The present invention relates to an electric resistor comprising a matrix formed from flexible, insulating material, and metal particles arranged uniformly inside the said matrix; and to a process for manufacturing the said resistor.
Electric resistors are known, which substantially comprise a matrix of flexible, insulating material, e.g. synthetic plastic, and metal powder arranged uniformly inside the said matrix. A drawback of known resistors of the aforementioned type, however, is that they cannot be employed as electric conducting elements in electric circuits, on account of the exceptionally high resistance they present when idle. In fact, the specific conductivity of known resistors, produced using various processes, is only high enough for them to be employed as electric conducting elements, when the resistors themselves are subjected to fairly high pressure. This is because the electric resistance of resistors of the aforementioned type falls alongside increasing pressure on the resistor, whereas, when idle, i.e. in the absence of external pressure, the said resistors assume substantially infinite resistance values. Furthermore, the electrical characteristics of resistors of the aforementioned type do not remain constant throughout the working life of the resistor, and are also difficult to reproduce productionwise.
To overcome the aforementioned drawback, resistors of the aforementioned type have been proposed whereby the powder distributed uniformly inside the said matrix consists of a mixture of powders of specific, controlled shape and grade, and, more generally speaking, having specific physical and chemical properties. Resistors so formed, however, are obviously extremely expensive, on account of the numerous operations involved for preparing the said mixture, and the high cost of the raw materials required for producing the powders themselves.
In some cases, to improve the electrical characteristics of the resistors, use is made of highly complex processes also involving numerous operations, as well as special equipment.